This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-175152 filed on Jun. 12, 2000.
1. Field of the Invention
The present invention relates to a brushless motor used as a blower motor of a vehicle air conditioning system.
2. Description of Related Art
One type of previously proposed brushless motor used as a blower motor of a vehicle air conditioning system includes a stator, a rotor and a circuit board. The stator is secured to one side of a motor.holder. The circuit board is secured to the other side of the motor holder and includes an excitation circuit for supplying exciting current to the stator. The circuit boar is covered with a case connected to the motor holder. When the exciting current is supplied to the stator, the rotor is rotated to rotate a fan to blow air.
During the operation of the brushless motor, excessively high internal temperature of the motor causes the exciting current to be reduced, leading to a reduction in an output power of the motor and also causes failure of electronic components. Thus, in the previously proposed brushless motor, a heat source (e.g., the stator or the elements on the circuit board) located inside of the motor is cooled with cooling air during the operation of the motor. However, in this case, during rain, car washing or the like, water droplets can be drawn into the interior of the motor along with the cooling air. Some such motors have a structure that restrains the water droplets from being drawn into the interior of the motor.
Specifically, with reference to FIG. 6, in one previously proposed brushless motor, a ventilation chamber 53 is defined between a motor holder 51 and a base case 52 connected thereto. Cooling air is drawn into an interior (stator side) of the motor through the ventilation chamber 53 and a guide hole 54. With this cooling air, the heat source located in the interior of the motor is cooled. Furthermore, as shown in FIGS. 6 and 7, a water reservoir 55 for accumulating the water droplets is formed in the ventilation chamber 53. In the water reservoir 55, a side wall 56 protrudes from a base of the base case 52. The water droplets drawn along the cooling air are accumulated within the water reservoir 55, so that the water droplets are not further drawn toward the interior of the motor.
In this motor, the motor holder 51 is not in sealed contact with the base case 52. Rather, the motor holder 51 simply abuts against the base case 52, allowing the water to flow through the contact surface between the motor holder 51 and the base case 52. Thus, the water can penetrate into the interior (stator side) of the motor through the contact surface between the motor holder 51 and the base case 52. However, as disclosed in Japanese Patent Application No. 11-121489, in the previously proposed brushless motor that is shown in FIGS. 6 to 8, water-flow interrupting holes (water draining portions.) 57a and 57b are provided in the connection or contact surface between the motor holder 51 and the base case 52 to restrain the penetration of the water into the interior of the motor. With reference to FIG. 8, notches 58a and 58b are formed in the base case 52. A water-flow interrupting hole 57a is formed by the notch 58a and a lower side of the motor holder 51, and a water-flow interrupting hole 57b is formed by the notch 58b and the side of the motor holder 51. In the water-flow interrupting hole 57a, a projection 59 projects from the side of the motor holder 51 to contacts, the notch 58a of the base case 52. With this arrangement, the water droplets penetrating the connection between the motor holder 51 and the base case 52 are directed downward, as indicated with an arrow in FIG. 8. The projection 59 is not entirely, continuously engaged with the notch 58a. In other words, a base end of the projection 59 is spaced from a base of the notch 58a. As a result, the water guided downward in the water-flow interrupting hole 57a is not guided upward in the water-flow interrupting hole 57a to further penetrate through the connection between the motor holder 51 and the base case 52. Similarly, in the water-flow interrupting hole 57b, the water is guided downward and does not further penetrate through the connection between the motor holder 51 and the base case 52. Thus, the water-flow interrupting holes 57a and 57b in the connection between the motor holder 51 and the base case 52 cause the water droplets to drop therein by gravity.
In the ventilation chamber 53, the cooling air flows toward the stator side. However, in the case of the brushless motor having the water-flow interrupting holes 57a and 57b, a portion of the cooling air leaks from the ventilation chamber 53 through the water-flow interrupting holes 57a and 57b. If the brushless motor is located near legs of a vehicle occupant in a vehicle cabin, the leaked cooling air may cause an unpleasant sensation to the vehicle occupant.
The present invention addresses the above disadvantages. Thus, it is an objective of the present invention to provide a brushless motor that includes a water draining portion for draining water out of the motor and effectively reduces or restrains leakage of cooling air through the water draining portion.
To achieve the objective of the present invention, there is provided a brushless motor including a motor holder and a case connected thereto. The motor holder includes a stator secured thereto. The stator rotatably supports a rotor. The motor holder also has a circuit board connected thereto. The circuit board has an excitation circuit for supplying exciting current to the stator. The case covers the circuit board and defines a ventilation chamber in cooperation with the motor holder. The ventilation chamber, includes an air inlet portion, an air outlet portion and a water draining portion. The air inlet portion is in communication with an atmosphere. The air outlet portion is in communication with the stator. The water draining portion drains water introduced into the ventilation chamber out of the brushless motor. The brushless motor provides a flow of cooling air passing through the ventilation chamber via the air inlet portion and the air outlet portion toward the stator for cooling heat generated during rotation of the rotor. At least one of the motor holder and the case has one or more guide ribs arranged in the ventilation chamber to define an air passage for guiding the cooling air from the air inlet portion to the air outlet portion. The water draining portion is located outside of the air passage.